1. Field of the Invention
The invention relates generally to a foundation and repair method and apparatus utilizing precast cylinder pilings with metal support rods extending axially through and bonded to the pilings to create a column which is sequentially driven into the earth to form an underground pier.
2. Description of the Related Art
One of the older methods for repairing foundations of buildings having slab-on-ground foundations uses drilled underground piers. Holes are drilled approximately eight to twelve feet in depth and filled with concrete. After the concrete has dried, jacks are placed on top of the pier and the foundation is brought to a level position. The jack is replaced by blocks, shims, and grout. A more recent and less expensive method is the use of driven precast solid concrete cylindrical pile sections, which are approximately one foot in height and six inches in diameter. These sections are driven into the earth one on top of the other to form a column or stack of concrete cylinders. The depth to which the bottom of the pier is driven into the earth depends upon the type of soil and zone of the seasonal moisture change. A cylinder having a larger diameter, or a pile cap, is a placed on top of the previously driven sections. Jacks are placed on top of the pile cap and the foundation is lifted.
The precast pile method relies upon the skin friction with the soil for its strength. It has the advantage of being faster since the concrete does not have to cure and precasting allows better control of concrete strength. A major disadvantage is that the one-foot cylindrical sections may shift and become misaligned during or after the driving operation. Different methods have been proposed for maintaining alignment between sections. However, most do not ensure that there is a least one support rod running completely through an individual piling section.
The precast pile in this invention is made up of piling segments that are driven into the ground one on top of the other. Each segment has a passageway running axially through each segment that aligns with the passageway of the other piling segment. A short support rod that is one-half the height of the first segment is placed in the passageway of the deepest piling segment. An intermediate support rod that is one and a half times the height of the first segment is placed in the passageway of the deepest segment next to the short support rod. A long support rod is positioned in the first and second passageways so that the long rod abuts with the top of the short support rod. The long support is twice the height of a single segment, so the long rod protrudes above the second piling segment a distance of about one-half the height of the second piling segment.
The method for installing the piling described above is made up of the steps as follows. A first piling segment is driven into the earth. The segment has a passage running axially through it in which a short support rod and an intermediate support rod are placed side-by-side. A second piling segment is driven on top of the first segment. A long support rod is then placed on top of the short support rod inside the passageway. Another long rod is placed on top of the intermediate support rod inside the passageway. The passageways are pre-filled with grout to secure the support rods in the piling segments. Additional pilings are driven into the earth, and additional long rods are placed and grouted into the passage on top of long rods already in place until the pilings are the desired depth. The short and the intermediate rods cause there to be at least one solid rod traversing each piling without a joint at an intersection of piling segments. This interfaces the rods at depths that are not the same as the intersections of the piling segments and helps to provide lateral support and prevent misalignment problems.